Existing utility grade electrical energy meters using isolated shunt resistor current sensors commonly use a conventional switched-mode power supply (SMPS) to power the isolated circuitry associated with the shunts. These SMPSes use either a ferrite-cored or an air-cored transformer. Ferrite-cored transformers can be magnetically saturated, making the meter susceptible to tampering from a powerful rare earth magnet placed on the outside of the case. Air-cored transformers are bulky, have low efficiency, and produce significant electromagnetic (EM) emissions, which must be contained by screening. Thus, there would be a benefit in the art to have a tamper-resistant power supply for isolated shunt circuitry that can also be low cost.